Electric organ



March 13, 1951 T. R. ELLEFsoN 2,545,023

ELECTRIC ORGAN Filed May 9. 1949 2 Sheets-Sheet 1 35 A 37 ATTURNEYSMarch 13, 1951 T. R. ELLEFsoN 2,545,023

' ELECTRIC ORGAN Filed May 9. 1949 2 Sheets-Sheet 2 7 mEwRERE/ Zg Ma fATTORNEYS Patented Mar. i3, 1951 STATES PATENT Q-FFICE' ELECTRIC QRGAN`VTheodore R.. Ellefson, Dayton, Ohio, assigner.l of; nnerthirdto HaroldH. SingerA and Que-tl irdtq. Morris P. Eelmamrboth of: Dayton, OhioApplication May 9, 1949, Serial No, 92dI :6-

(Cl. S11-1.01)

9, Claims., 1;

The present invention relates to apparatus for producing sustainedmusical sounds and tones. more particularly to toy organs, although theprinciples o1` my.- invention-.can be equally appliedtoorgans-offconventionatsize or to organattachr'nentsi'ou any. standardpiano,

Manyattempts have-heen. made heretofore to provideani electric orgaxu ofpractical design, usingl eithep a.- single controllable oscillator or asepa-rate pre-tuned xed oscillator for each of the various notes o! theregister, butin. every case tl' mak-ingA andnbreak-lng off the; circuitshas necessitatedi complicatect. and impractical struc- Evcn, inA thosecases.- where. the sustained n'ptes are produced by a single thermlonicoscil ltoxiim which. thepitcli-L is changed by a. variable rsistanceunder thecoptrql. ot the playing keys, thcftune changing.devices-.are.inemcient, changeable-with temperature. conditions. and keypressure, and in general, so expensive as not. to b e ilaptableito toy.-organs. 'Eheppimary objectoi the invention is to pro.- vide; animprovedelectric4 organ op organ attach.- mancia which theoperating parts are soeectivei. yeiiinexpensive; as to. be readily. adaptable tomseas-.a-toy..

Anotherobject: is; to. provide an: improved toy electric organ4 inwhichCthe.: are so few in number and of suchsimple, design as to .be rela.,-tiuely. inexpensive.. thus` permitting the toy to be soldatiareasonableprice.

A stili-f-urther-obifect isto providen improved electric, organv ororgan. attachment. employing an electric oscillator system of standardtime, adapt.- ble, for alternation.- curifent. and with simple changesusable with direct current energization,

-tosethsrwith. a hex-board oieither limited or standard length.

further object is,tofprovidc.11i-toy4 orga-n which @euries a. number:of' tinte-stops. Similar; t0 a C011- ventionak orga-n, andf 1x1-.which'the tone registers are effected by. control knobs. or switches. servtoraiseor lower theaverage-pltch. 0f the organ in accurately.pre-.determined amounts.

An additional; object is to provide en4 improved toy. organ which willincinta-inthe predetermined tone relationbetween notes. and remain intune regardlessof changeset' ambient temperature or humidityconditions.4 y

A stlll further object is to provide a. toy organ or study constructionwhich can be readily dis- ,c .ssemblecLV parts replaced, and which canbe manufactuxeci` in quantity production with complete reproducibilityofA operation and tone per unit.

Other objects and features-willbe apparent as the following spaeiication is perused in cannet: tion with the.ac xompanying drawings,in which;

Figure. l: represents. a. perspective View of the improved organ shown.in; toy form;

Figure 2 is a s ide,- elevational view of the organ with. parts brokenaway to reveal the make. and break` mechanism Lor controlling theproduction of the tones;

Figure 3 shows. the keynboa-rdi and associated grid resistors. with the.switch mechanism. indi:P cated diagramm atically. for clearness;

Figure 4 isafragmentaryview4 of a. modified formoi-4 theindii ridual.switching devicesoperated bythek8y8 i Figure show s a system including.-a series of reactancss, spec condensem im:-4 changing the pitchoithe.'`miesas a whole;

Figure 6=is an. elecrical system includipg the oscillator, rectiil enand: loud4 speakeremployed. in the improved.- organ for producing themusical sounds;

Figure 7. show-'s a modilled system, somewhat similar toA thatillustrated in 6, but inicluding a difiere ntarrangement ot oscillatorand rectifier devices, and;

Figure 8 depicts a modied form: of thetone changing conde;

Referringmoroparticular-iwf t0 Figs: l: and; 2, reference charozter I2designates the sides of a compartment p: eferablymaden of an ornamentalwood and suili ciently thin as.- to havegood resonancecharz ctcrlstics.Theseslde. members are cut to an il regular shapewith an inwardlytapering edge :s indicated; at 2; which meets with a horizont: il:portion. 3- to. give. the effect of an ordinair-yl ors on. console inminiature. with. a place left for im aginm Iootpedals. These. side.pieces are provi led-f with. avexticalportion indi.- cated at 4 and' s.combined steppeds-baclrportion indicated. at 5; t] ne. latten serving-toaccommodate a series'of' keysindicated'A at 6. black and white noteswhich ear-.end slightly. above thevertical side portion I. Thesesldesare connected4 together atthe to; by a transversepieee- 1- of thinboard, plywood. etc.. and by a'narrow. 'vertical piece. 8. just abovethe keys. A thin board.- 9 connects the por tions 4 ot the end; membersand, `in addition, th i. vertical portion. tu. Similar pieces of woodlextend between the :fe-entrant portions 2:, 3 of the end members; andthe com.- partment or boi: is completely .closed by means of a fairlythicl:` back memberll..

There is a hor zontallyextending shelf- |12 made of wood and ,postionediust below the. upper edge of the vertical piece 9, this shelfextending for the full width of the box and being made somewhat heavierthan the side and the front portions as indicated in Fig. 2. A groove I3is cut into the shelf member along its upper surface and about midwaybetween the front member 3 and the back member'II 'to receive an uprightmetal bar I4. Playing keys- 6, preferably constituted of hardwood, andpainted white and black, as in the case of an ordinary organ. rest uponthe bar I4 an'd are located by means of a notch extending transverselyacross the lower surface of each of the keys. The latter are held inposition against the bar by means of looped springs I5I the lower leg ofwhich is secured to the shelf I2, and the upper leg is afiixed in anysuitable manner. as bysimple pressure, to the upper surface of theplaying keys.

The convolutions of the springs preferably rest on the upper suriace ofthe shelf and openings I6 for receiving the short vertical portions ofthe springs just below these convolutions are provided in the shelfmember. Thus. it is seen that the eiect of the spring I5 is to press therear portion of each of the playing keys, black and white, downwardlytoelevate the front or playing surface of these keys. There is a blockor bar of wood I1 secured within the corner oi the vbox portions'l, 8 towhich is attached an angular metal-'strap I8. The lower or bent portionof this strap is positioned directly above a portion of each of thesprings I5 so that when the keys 6 are de-pressed to elevate their rearportions the springs I5 make respective contact with the bar 'I8a's"long as the key or keys remain de-pressed. :'A conductor -ISissecured to the bar I8 by means or' a screw 20,-` this conductorpassing through an insulated cable 2|, to an electrical system'whichwill be described presently. Conductors 22. as many as there are springsand playing keys n', are connected respectively to each 'of the springsand secured thereto by means of a screw indicated at 23. Theseconductors also extend to an electrical system.

As shown in Fig. 1. there is a loud speaker 24, convenient-ly located inthe re-entrant iront portion and also a pair of levers 25,-2.i, each ofwhich may` have two (positions oifwhich one per lever isindicatedait-21.48. The purpose of the loud `speaker and levers willbe--described in connecftion with the system. l Referring to Fig. 6,Ihave illustrated a typicalform 4of electrical system that can be used.for translating the downward movements of the respective keys 6 intomusical sounds at the loud lspeaker. In this gure, reference character23 designates a -combined tetrode and rectier tube provided with anindirectly heated cathode. Tubes -of this character can be procured onthe fopen market. The rectifier unit is comprised of Jan anode 30, a.cathode 3l and a iilament or .heater 32. The 'tetrodeportion -of thetube in- Acludesan anode 33, a'screen grid 34, a control grid ,35; a-cathode 36r anda lalnentary heater 31. The 'grid-34 is connecteddirectly tothe anode 33. The `lamen'tarly''heaters4 31 are connectedtogether .across the mains -;38 of any suitable source of 'alternatingvoltage. The anode 30 of the rectitone changing system indicated by thedot-dash vline 38.

rectangle 42. then through the primary coil 43 of an audio frequencytransformer 44 back to the cathode 36 through a conductor 45. Thecathode 36 is connected to the conductor 45 and the cathode 3l isconnected to the same conductor through a resistor 4I. One terminal ofthe secondary '4B of the transformer- 44 is connected through aconductor 41 to the anode 3.3 of the tetrode. The other terminal of thesecondary is connected through a conductor 43 to one side of the primarycoil 49 of an audio frequency transformer. The other side of the primary49 is connected through 'a conductor 5U to one side of the A conductor45 is connected between the cathode 3| and the conductor 50. A radiofrequency condenser 5I is shunted across the winding 49. A secondary 52of the transformer Slla is connected to the` energizlngcoil 53 of a oudspeaker 24 of anyljsuitable and well known A circuit of the type shownand describedin connection with Fig. 6 constitutesan audio fre? quencyoscillation.generator...the. feed back between the grid and anodecircuits ,-being; obtained at the windings 43, 46. 'l'he tetrooe.portion of the tube 29 serves to translate the direct current furnishedby the rectifier portion of the tube into audio frequency oscillationsso that the oscillator and the rectifier portions of the..ltube performtheir functions'more onle'ss independentlynfone another to provideconsidrable eiiiciency in changing-the alternating.' current attnezmains 38 into higher Vfrequency currents of a musical range in thecoil 43..; r` .z'i

The frequency developedlgpy` .the .generator is determined in part bythe combined gridresistor 54 and the combined grid condensersicontainedwithin the rectan'g1e'..42 .which-'will be described presently.

Obviously any change in theresistors or condensers will cause thefrequency of. the;generator to either raise or lower and thusproduce achange in the pitch of the musical;.,note.enlitted 1.at the loudspeaker. The grid leakI -54 is constituted-of a large number ofindividual resistprs'54a interconnected in. series and bridged-betweenthe g-rid 35 and the conductor 45.- Connections-22 are taken frompoints, preferably equi-'dist'antly spaced between theseveral-'resistance unita-these conductors making contact'. withtheindividual springs I5 (-Figl 2)." The elementsI'S-whichffareindicated'as switches-iii' Fig. 3 correspondl'with the .circuit makingportion of the springs I5el-n Fig. 2 which'make.:a'nd'-break-'contactwith' the iongitudmauy extendinggibaf 1a. 'The latter connected through'ther conductor I9' to" -th'e cathode 36 of the tube 29.

It is obvious that 'as'a'hyof the keys '6 are-idepressed and contact"is" made between the ends of theindividual springs' I5 and theplataoi-ibar I8, variable amounts" of= thrsistoii'is-shortlcircuited bythe bar I3 tochangethe magnitude of the grid resistance and thuscliangethe fre'- q'uency generated by Alairetulipe251. TheV maghi.- tude of thevarious resistor units 54a is; so pre"h vdetermined vasfto give :theproper `variation"in't`one from note to note, and obviously thisvariation remains the, same .regardless of any temperature Aor humiditychanges that mi'glt effect .the'frey sistance as a. whole, boallse thepants-change relatively. in the same amollrit.. Thus, increases or."lecrea-s'esV of resistance in .fb'c'ed amounts .are effected bymanipulating th`e playing keys@ A sin that the generated frequencies arealways in rela:-

ill tive' tuneas translated ?intosoundlmpul'$esfatthe loudspeaker:

In order'4 to prevent". the" produc-twin` oif a: sus-'-` tainedaudiabl-notvduring'ttie'eperiods thatthe keysaren-ot'beingy depresseditzlk-dtnlrablertorsa predeterm'ine the constants: off" thee oscillationgenerator tha-tithe' latten will gener-:artisI oscilla'- tions onlyof'ihaudible-frequency: 'Biis'canflie accomplished: by proper "selectiontl-i magnitude" of' the-grid resistor' i asa vvlioler:n when thevalut?loi thisA dcl'feased as b'y bengpartially sliortci-rcuited? bythe liar Il upon manipulaigion'ofthe-lieys; thgeneraton'willdevelop'oscillatlonsfo!c am audllilef olarac-tenaand.

these oscillationsjjwillrevert tormaudiliilityfwiien none ofl tlic'-remainY depressed; It` portant' that any direct*l current component-loftle-generator'output'sliallibecompletelyexcluded fromthe energizinglcoil` 531 of tlielbud. spegler.` in order that' there siiall" be ntl'excesive on tliegenerator-'wlen a* child" would* Inadjer tentlyleavethe'forgan connectedT tothe electric outlet. but more especially;tlrprovidcV mier purity'of-tone-hr the speaker-without the'hairlperingeffct'ofi'rectiileddlrectcurrent In order tot give' as mucltto1 the-4 characterA of thetones: as possibleeih a: tom.I-liaveprovidedastepstep variable condenser in the grid ReferringrFl'g:'5, seris'of condensei's- 55` are= in. parallel' to. the grid I5- and1brought o uIf. to`4 oontaetsfl It A pair of'l'evers-f 25E 16 pi'vot'edatflii iis"I arranged to male-c'ontactiwithfany one oond'onseroi'tliegroup. areh eonneetedl in'. parallel through a conductor Hitos-once.slileror-tiiepriimary windingy 'Illiusfbymovingoneon the-otherotheseflevers toconta'ct anyoof thetcondcnsermsif thelatter iseil'ectively thegrl'dioiicuit-,thereby serving tochange emitted'bytheloudfspeaen- Ihiothen'words, .this register maybe toranyonefol'asoprano, contralto; liariinnedepending on which ofthe'l'evers-ispperatedandfgere Iorewhich of' the oondonsersf are. into`r thc'agrid" It plyiiig: the; organ'camtlierefowobtaiiwonsiierablewariation in'the character ofthe enhances the of l various other" ofcondenan-inserting apparatus may be empfyed andicncrtl'xertypicalexample is showin 'inf Eig: .8. in.- wliiciir com densa-a n are oilsurement-@the various. 'is'- lnad'e' to anyone .aA lever 59- xav-hicli`one: of.' terminals 8l connected to -on'e side therespectivecorrd'ensers; M leverwmawberconnected toy the: winding I3,,andthemthensitfeaottne corr densexs= is connected thronghi 6I to. thegrid*` conductor-12.

Still? anothertype occiilatiom generator that can be employedilnaccordancwithf-myfinventlcn isfshowninzF'lg.' '1i 6 in using arechner-'GS separate fronrthe oscillation gcnersrtx'hf*6KV "Elicsetubes'u; Si' are also of'standardftypes. .readilyprocureable-cmthe market',endl the heat'orsf'l. 32. -norxnully-4 takev a lower voltagethan 25?.showm imFi'gf. 6 'and i'orthatzroason .may-have tn-inclnde-a-voltagereducingfresistorl Inasmnclnasstlrernemaimng elements sho1vn.in\-.this,ngncevareV similarI tosthose describetf inconnectionf with Fig; :B2such; 4elements' have: been. given corresponding' referencel characters.

Inge-neral, the system inFlg. ''operates similarlyto that-d ascribed inconnection with Fig. 6 ln-t'hataudio f1 'equencyoscillations aregenerated inthe-tube 64 which is supplied with rectified voltage by thetube 63. The frequency of these oscillations-"is momentarily changed byvarying the magnitude of the resistor 54 upon de-pressing any-f one of`the keys E and the tone register can changedfrim soprano to contralto,etc. by simply changingV the value of the grid resistor in the mannerdescribed in connection with Figs. 5"-and 8. Itwil be noted that thesystem shown irl-Fig.' 6'is a little more compact than that in Fig.7'but vthe litter offers the advantage in case either the oscillationgenerator or the rectifier tube needsre; lacement, then only one of thetubes hasftobf replaced and does not involvea combined osci lator andrectifier tube which would. be moro expensive to purchasel on themarket;

While I pren :1' to employ the contact making and breaking :tructureshown in Fig. 2, which is-simpleto co nstruct, less likely to get out oforder andyet is very eective, nevertheless other structures can.l|e.usedfor the same purpose. In

4', the playing keys lA are fulcrumed on the bar. Il. and inst` :ad ofemploying a. coil spring for holding` the. playing ends of the keys inan elevated positic n. I may employ a compression spring 66. for cach..key positioned between the bar IA and; the innermost end of the key. Thespring is locatei in a circular socket 61 formed ihileach .oi-'thek sysVand;enters a similar socket at theztopiormed': n avwooden bar 68 whichextends the length of. th aorgan. The bar is-supported by metal bracketsB9. secured tothe top cover l at thetend or side members I of thecompartment. Inverted C-sha1 ed straps in may be secured to theA lowersurf: ce of the shelf I2 and passing upwardly throunh the opening IE toextend over the inner end. cf each key 6.

Whenthe latt 2r is depressed about the fulcrum It the upper horizontalend of the strap l0 is causedto move upwardly and to make contact with.a metal. strap I8 which is secured to a wooden bar 'II u hich extendsalong the length .of the: box., 'I'his bar is electrically connectedthrough-.conduc '.or I9 to the cathodev 3S o f the oscillator, while theclamp 10 is electrically connected through the conductor 22 to the grid35 of theoscillatoi. Thus the spring 65 tendsto keep the;pla.ying end ofthe keys in. an elevated position and when the latter. is depressed thespring is comprtssed and the upper end of the .strap 'I0 contacts thebar IB.V Inasmuch as the conductors 22 are connected to xed contactsVon-'thcgrid resis sor 54, the downward movement ofthekey-willcz usefrequencies of diilerent tone value to beA generated by the oscillatorin the same manner a.: described in connection with Fig. 2;

Another featul e of' my invention is in controlling the generaton ofoscillations to only that periodlwhen any one of the playing keys isdepressed rather tlan have the oscillator continuously generate os:illations when none of the keys are-depressed and in that mannerinvolve energy that -is not being used for audible sounds. Each of'theplaying keys carries a metal contactfTZ which, when the key isdepressed, is adapted to contact a metal strip 'I3 extending along theshelf I2. The b: .r is connected through a4 conductor 14 passing throughthe shelf to connect with one end' of Ihe winding 43. The individualcontacts=l2 are connected through avery flexible 7 wire'lS to thecontrol grid 35 ofthe-oscillator, this wire passing through an openingin the shelf I2. The arrangement is such that the grid circuit of theoscillator is open at all times except when any one of the keys isdepressed, so that the oscillator will generate oscillations only duringthe time that any key is actually pressed downward. This arrangementconserves energy and obviously can be applied to the key depressingstructure shown in Fig. 2, if desired.

The electrical inertia of the system shown in Figs. 6 and 7 is so smalland also has such a sharp cut-off that even if any appreciable timeelapses between depressing successive keys, the oscillator will notoscillate during this small, almost imperceptible periodof time. The useof the make and break contacts l2, 'I3 are additionallydesirable whereit maybe advantageous to prevent any' residual current from passingthrough the loud speaker so that the latter is effectives-only duringthe time that the musical notes of desired tone are being emitted.

" It will be understood that various modications and arrangements instructure could be made without departing from the spirit of myinvention and, accordingly, I desire to comprehend such modificationsand substitutions of equivalents as may be considered to come within thescope of the appended claims.

Having thus fully described my invention, what Iclaim as new randvdesire to secure by. Letters Patent, is:

- 1. A vmusical instrument comprising an audio frequency voscillationgenerator, including .a thermionic device and a contained grid andcathode, a. grid resistor for-said tube, said resistor being subdividedinto predetermined portions which cause the generator to developoscillations o'f dierent tone frequencies, means including playing keysfor individually connecting-preselected subdivisions of said resistorvto the cathode of said generator, said means including an equipotentia1metal bar connected tof-the cathode, contacts on said keys connectedrespectively to said resistor subdivisions, and adapted to contactthebar when the respective keys are depressed, and an audio receivingdevice responsive to` changes in said frequency caused by 'thedepressing movement of said keys.

vidually to portions of the grid resistor, an: equi;- potential metalbar connected to the cathode or the tubeand located' in contact-makingrelation with'respect to said springs when the keys are depressed, and asound-producing device in the output circuit of said generator.

3. A musical vinstrument 4comprising an audio frequency oscillationgenerator, including a thermionic device and' a contained. grid' andcathode, a grid resistor forsaid tube, taps taken from said resistor, atpredetermined positions, means including playing keys for connectingpre-selected'taps to the cathode-of said gener- .ator to cause thelatter to develop oscillatQns sluiting-make an.; breek contactsat .theend-of the keys which 'are respectively connected to saidresistor'tapsf--springs for.V maintaining the contacts -xopen until thekeys areoperated. a sound-producing device inv the output circuit ofsaid generator and means for supplying thealternating-ourrent;componentlonly of saidgeneratonte the sound-producing device.

'1-4. A; musical instrument comprising an yoscillation generator.inc1uding a thermionic. device and' a contained gridfand cathode, a resistorconnected ybetweenthe cathode and grid-of said tubeandhavinggamagnitudesuch that the oscillationgeneratorywilldevelop oscillations outside therange-of.- audio.. fre quency,.-taps. taken from said resi s t 1f..v atpredetermined positions which-miese mated thats-'when resistance asdetermined-.atthat-position is connected between the cathodei and grid-of-the tube, the oscillator will generate .audio .frequencies having a-tone determined by thefposition-of the taps, means including-playing.keysfons-connecting predetermined -taps directly-.tombe cathodein =order to Asliort-circuit lthe .resistance intervening -betweentha-.cathode 4and thef selected tap and therebychangethetonefr-.equencyof the gen'- erator, said .meansi luding make and breaklcontacts at th ,.endsgogfthe keys which are respectively. connected-to.-said resistance, taps, means fori maintaining-the contacts openuntil any one-of ;the keys is operated, a sound-producingdevicenjtheoutputcircuit of said-gener- .a-tor and-means for supplying thealternating current component only of said-generator to the .zkeys down,said springs being connected =indi ..60

5. A musical instrument comprising an audio frequencyoscillationgenerator, -includinga ther-mionic gdevice '-anda contained--grid .and eathode, a grid fr esistor connected-between said grid-andcathode..taps taken from said resistor .at -predeterminedlpositionspmeans including playing keys for connectingpreselected taps tothe cathode -of- 4saidgenerator --to lcause the vlatter to developoscillations of different tone frenuencies, said means .including makeand .break contacts ait-,the end s of the keys whichL are re'-spectivelyconnected .Aoi-'said resistance taps, means-ffosmaintainingthe contacts-Lopen until any one of the keys :is depressed, lnsound-pro- --ducing-devicelinr-the output circuit of said generator.-rneans-fprchanging the tone; register as .ai-whole o-.theinstrument-and-means for sup.- -plying the alternating curreutIcomponent only of said-generator to the sound-producing dev-ice. 6; Amusical .instrument comprising anaudio :frequency ;oscillation.generator.- including a Athermionic -device'iA and --a' contained-grid--and ca-thodefa--grid-resistcr connected between said grid and'cathode,.;taps taken from said-resistor ,fa-t predetermined. positions,--means including playing keys for connecting preselected taps :to thecathodeofsaidf'generator to-cause the '--latvter-todevelopgoscillatipnsof different tonel frequencies,said-means-inciuding make and break contacts attire-ends ofpthe. keyswhich are re- --spectively connected to4 jsaidfresistance taps. meansfor maintai-riir1g'` contacts open until any one 'of the keys' -isfdepressed, a--sound=pr o duc-ing device inthe output circuit of saidgenerator, ,-meansfor supplying .-to saldsound-pro.- d-ucing device vtheoscillations of different tone -freq-uencies only., and means. forchanging-fthe toneregister as" a whole-fof theV instrument. said lastmentionedmeans-comprising -a plurality of .of different tonefrequencies, said means lx1-.15 grid condensers of differentcapacities-,zone oi which is selected by a lever on the instrument togive the desired change in the tone register.

7. A musical instrument comprising an audio frequency oscillationgenerator, including a thermionic device and a contained cathode, gridand anode. a grid resistor connected between said grid and cathode,means including a rectifier tube for energizing the circuit between thecathde and anode, with rectified alternating voltage, taps taken fromsaid resistor at predetermined positions which impart changes in theconstants of the oscillation generator such as to provide changes in thetone frequencies developed by the generator, meansl including playingkeys for connecting preselected taps directly to the cathode and therebyshort-circuiting the portion of the grid resistor between the selectedtap and the cathode, said means including a, resilient metal strapsecured to the instrument and serving to press the inner end of eachplaying key downwardly. said keys being fulcrumed on a common bar sothat the Straps additionally serve to elevate the playing end of thekeys on the fulcrum, and a metal bar positioned directly above saidmetal strap and adapted to be contacted by the strap when any one of thekeys is de-pressed against the pressing action of the strap, said barbeing connected to said cathode and said straps being connected to thetaps of the grid resistor, a sound-producing device in the outputcircuit of said generator and means for supplying to said deviceoscillations of diierent tone frequencies to the exclusion of therectified alternating current.

B. A musical instrument comprising an oscillation generator havingconstants including a resistor which normally require the generator todevelop frequencies outside the range of audibility, taps on saidresistor at positions such that when a. connection is made from anypredetermined tap to the cathode, the constants of the generator causethe development of oscillations of audio freqiency of dierent tonesdepending on the particular tap selected, means including playing keysor selecting said taps, said means including maize and break contacts atthe ends of the keys, s: ,id contacts being connected to said taps,means :"or maintaining the contacts open until the key; are operated, asound-producing device, and means including a transformer in the outputcir :uit of said generator for delivering audio frequexcy of differenttones only to said device.

9. A musical instrument comprising an audio frequency oscillationgenerator, including a thermionic de vice and a contained grid andcathode, a resistrr connected between the cathode and grid, meansincluding playing keys for changing the magnitude of said resistor inorder to cause the oscillator to generate oscillations of different tcne frequencies, said means including make anc' break contact-s at theends of the keys which interrupt the circuit to the respective taps,saii oscillation generator being normally rendered inoperative, andmeans associated with said keys for causing the generator to generateoscillations at frequencies determined by the preselection of saidresistor taps when the keys are successively depressed, said meansserving, to restore the inoperative condition of the generator when thekeys selectively return to ther original undepressed position.

THEODORE R. ELLEFSON.

l LEFERENCES CITED The followil 1g references are of record in the illeof this patent:

UNITED STATES PATENTS Number Name Date 1,543,990 de Forest June 30, 19251,782,542 Miller Nov. 25, 1930 2,301,871 Hanert Nov. 10, 1942 2,470,148Demuth May 17. 1949

